1. Field of the Invention
This invention relates generally to a recording and/or reproducing apparatus for wide band video signals and, more particularly, to a system for compensating drop-outs during playback of such signals.
2. Description of the Background
A multi-channel recording system has been proposed for recording wide-band video signals having a luminance signal bandwidth of about 20 MHz and a chrominance signal bandwidth of about 6 MHz on an optical disc. Such wide-band video signals are found in the so-called high-definition television (HDTV). The video signals are encoded prior to recording and are distributed into plural channels and then recorded on parallel tracks formed in correspondence to the plural channels. The reproduced signals are decoded back to original video signals in a reproduction mode. Through use of this system, even though the rotational speed of the recording medium is not high, the rate of recorded information per unit time is increased by the number or recording channels. Therefore, a wide-band video signal can be recorded and reproduced using known record media and associated hardware.
If there are two channels, a pair of parallel tracks are spirally formed on a disk. More specifically, the video signals are simultaneously recorded by optical heads arranged in parallel relative to the corresponding tracks for the two channels during the recording mode. Subsequently, the video signals are simultaneously reproduced from the tracks by the parallel optical heads in a reproducing mode.
It has been found that degradation of an image due to a signal drop-out caused when high-definition video signals are reproduced tends to be more conspicuous compared with the effects of such drop-outs when normal video signals are reproduced.
In order to compensate for drop-outs a system has been conventionally employed in which a one horizontal scanning period (1H) memory, or 1H delay line is provided. Upon the occurrence of a dropout, the drop-out signal portion is compensated by signals of the immediately preceding line, which have been accumulated in the 1H memory or delayed in the 1H delay line. Although this system is relatively simple, if drop-out compensation is performed in an oblique line portion of the reproduced image, a discrete step may undesirably appear in that oblique line of the reproduce image because of the repeating of the preceding line data.
In another compensation system, a 3H memory is used, wherein if a drop-out occurs, compensation is performed by using the mean value of the memory contents, which are based on the immediately preceding line and succeeding line periods of the drop-out line interval. When this system is employed, a discrete step in the oblique lines of the reproduced image is not so conspicuous as in the case of the 1H memory. Nevertheless, some degradation of the image is still present. Such degradation is still unacceptable in high-definition television.